1. Field of the Invention
This invention relates to an internal-combustion-engine ignition device and, in particular, to an internal-combustion-engine ignition device equipped with an ion-current-detection-diode assembly and an ion-current-detection unit for detecting ion current generated in the associated cylinders.
2. Description of the Related Art
FIG. 17 shows the construction of a conventional internal-combustion-engine ignition device. In the drawing, numeral 1 indicates an ignition coil including primary and secondary windings 1a and 1b; numeral 2 indicates a power transistor connected to the primary winding 1a and adapted to conduct/interrupt primary current; numeral 3 indicates a distributor cap including a central electrode 3a connected to the negative-polarity side of the secondary winding 1b, and peripheral electrodes 3b which come to face each other by turns through openings as a distribution rotor 14 rotates, which rotor is in contact with the central electrode 3a; numeral 4 indicates ignition plugs respectively connected to the peripheral electrodes 3b; numeral 5 indicates a power source constituting a bias means for applying positive bias voltage to the ignition plugs 4; numeral 6 indicates a resistor connected in series to the power source 5 and serving to convert ion current to voltage; and numeral 7 indicates an output terminal for detecting the voltage generated at the resistor 6, the output terminal 7 constituting, together with the resistor 6, an ion-current detection unit 12 . Numeral 8 indicates diodes for obstructing reverse current; and numeral 9 indicates signal-take-out-diode assemblies including the diodes 8, the diode assemblies 8 being arranged on the outside of the distributor cap 3 in the same number as the cylinders . Numeral 10 indicates an engine, in the upper section of which the ignition plugs 4 are mounted; numeral 11 indicates a signal generator for detecting the turning angle of the engine 10; and numeral 13 indicates a computer unit for controlling the ignition timing, etc., to which computer unit the output of the ion-current detection unit 12 is supplied.
Next, the operation of this conventional internal-combustion-engine ignition device, shown in FIG. 17, will be described. When the power transistor 2 is turned off to interrupt the primary current of the primary winding 1a, high voltage for ignition is generated in the secondary winding 1b and applied to the central electrode 3a. This high voltage for ignition, applied to the central electrode 3a, is propagated through the distribution rotor 14 and the openings to the opposed electrodes 3b and, further, to the ignition plugs 4 to cause discharge between the electrodes thereof, thereby igniting and burning the air-fuel mixture in the cylinders (The current path in this connection is indicated by an arrow a).
With the combustion of the air-fuel mixture, ionization occurs to generate ions. After the above-mentioned discharge, the electrodes of the ignition plugs 4 function as ion-current-detection electrodes, and positive-polarity bias voltage of the power source 5 causes migration of electrons and positive ions, thereby generating an ion current. The generation of this ion current enables the voltage generated at the output terminal 7 to be detected, thereby making it possible to confirm the burning of the air-fuel mixture (The current path in this connection is indicated by an arrow b).
In this conventional internal-combustion-engine ignition device, constructed as described above, it is necessary to provide an independent diode assembly 9, including the ion-current-detection diode 8, for each cylinder. Further, the ion-current-detection unit 12 is arranged independently from the other components, such as the ignition coil and turning-angle detection unit, resulting in a complicated ignition-device structure and high cost. In addition, there is the necessity to ensure the space for the diode assemblies 9 and the ion-current-detection unit 12, resulting in difficulties in terms of layout inside the engine room, which, nowadays, is usually rather small. Further, this conventional structure involves a large number of parts and is rather poor in reliability.